Patent GB-707635-A (GB)
Title: Magnetic storage systems for electronic binary digital computers
Inventor: WILLIAMS FREDERIC CALLAND
IPC: G11B19/28
Filed: 1949-03-01
Abstract: 707,635. Digital electric calculating apparatus. NATIONAL RESEARCH DEVELOPMENT CORPORATION. Feb. 16, 1950 [March 1, 1949], No. 5633/49. Class 106 (1). [Also in Groups XXXVI and XL(b)] In an electronic binary-digital computor utilizing a temporary storage system and a clock pulse generator for synchronizing various operations, a magnetic storage system is provided comprising at least one rotatable drum on which signals representing binary numbers can be stored in circumferential tracks by a number of fixed recording heads, a motor capable of rotating the drum at a speed in excess of a predetermined speed, means for deriving a given train of signals from the clock pulse generator, a series of reference signals forming one of the circumferential tracks which, when the drum is rotating at the predetermined speed, induce in a corresponding recording head signals in synchronism with the given train of signals, and means for producing, in accordance with the relative displacement of the two trains of signals, a control current which energizes an electromagnetic eddy-current brake cooperating with the recording drum. The clock pulse generator 1, Fig. 1, operating at 100 Kc/s, supplies, through frequency dividers 6, 7 (preferably of the type described in Specification 582,758, [Group XL]), a blackout waveform generator 8 comprising a multivibrator or flipflop which under the control of the two frequency dividers produces an output repetitively at one voltage for 400 Ás for the scanning of one line of C.R.T. storage 29, followed by a different (black-out) voltage for 50 Ás during fly-back. The black-out generator also controls a square wave generator 12 which is used for synchronizing the magnetic store. The magnetic store 30 comprises a nickel-plated layer on a brass drum which is rotated at constant speed and co-operates with magnetic writing and reading heads 26 for recording or reproducing circumferential signal tracks round the curved surface of the drum as described in Specification 707,634. Any circumferential track can store in the form of pulse signals all the data which can be stored in one, 32-line C.R.T. memory. For the purpose of synchronization one circumferential track 31 has stored upon it 64 short pulses corresponding to the leading edges of the black-out pulses of the C.R.T. storage system. The intervals between the pulses are preferably magnetized in the opposite longitudinal direction. A transient pulse produced in the pick-up head 28 by each recorded pulse is amplified by units 13 and 15 and fed to a discriminator 17 where it is compared with the output 16 of the square wave generator 12. Discriminator.-The pick-up signal i, Fig. 2, applied to the grid of a normally cut-off valve V4, Fig. 3, causes the valve to conduct for a short period of time during which the cathode current in a twin triode V2a, V2b is increased tenfold, the course of the current through the valve and the direction of flow in the primary and secondary windings of a transformer T2 depending on the relative voltages on the respective grids. The grid of valve V2b is held at + 110 V, while the grid of V2a is subject to a square waveform g, Fig. 2, due to the input f from the square-wave generator at 16. The secondary winding of the transformer T2 is connected through two D.C. isolating condensers and biased diodes D1, D2 to a reservoir condenser C1 whereby any departure from synchronism will give rise to a D.C. voltage along the line 18 proportional to the displacement. This error signal is fed into a servo-amplifier and applied to the stabilizing network centred on the virtual earth simulated on the grid of the feed-back valve V5. Integral and time-derivative control is provided by an anode to grid feed-back loop. Eddy-current braking coils 20, equally spaced near the outer edge around a circular face of the recording drum, are arranged in parallel with the anode load resistor R5 of valve V6. The synchronizing action may be suppressed (e.g. when " writing " on the drum) by applying a negative voltage to the suppressor grid of V4. A course synchronizing control, operating once each revolution of the drum, is also described. In addition to those mentioned above, Specifications 682,156, 651,591 and 705,479 are referred to. Specifications 645,691 and 705,474 also are referred to.